In the production of oil and gas and activities pertaining thereto, corrosion of well tubing and related conduits for conducting oil and gas, or fluids injected into the earth to stimulate the production of oil and gas, is a continuing problem. For example, in crude oil production from wells which extend several thousand feet into the earth, corrosive activity may be occurring at various intervals in the production tubing strings, for example. It is important to be able to monitor this corrosion so that remedial action may be taken to replace the corroded tubing sections or by carrying out a suitable process to prevent further corrosive activity from occurring which might result in tubing failure. However, detecting corrosion in a tubing string which extends hundreds or thousands of feet into the earth, without withdrawing the tubing string from the well, has heretofore required conveying tools on cables, sometimes known as wirelines, through the tubing string to be inspected. These processes are complicated and expensive and in some wells have been virtually impossible to carry out.
The above-referenced U.S. patent applications, both assigned to the assignee of the present invention, contemplate the placement of certain sensing or measuring devices in a fluid production well. One advantageous point of placement of sensors has been determined to be that wherein suitable devices are disposed on retrievable gas lift valve assemblies which may be inserted into the well tubing and disposed in spaced apart sections of tubing known as side pocket mandrels. Typically, fluid production wells which are utilizing gas to assist in lifting production liquids to the surface through the production tubing string employ a plurality of gas lift valve assemblies disposed in spaced apart tubing sections comprising the above-mentioned mandrels. Accordingly, the present invention takes advantage of the concept of placing a particular type of sensor on a gas lift valve assembly which may be interposed in a well tubing string. Since several gas lift mandrels, up to twenty, for example, are typically spaced throughout the length of a production tubing string for an oil production well, these devices can serve as a point of placement of a suitable sensing system which may be used to measure corrosive activity on the tubing string including the gas lift mandrels themselves.
The prior development of unique arrangements of downhole sensors for use in measuring certain properties of fluids flowing within deep wells has also fostered the development of an arrangement wherein predetermined sections of the tubing or casing making up the well structure may be monitored by a suitable instrument assembly to determine if corrosion is occurring at selected points within a well. It is to these ends that the present invention has been developed.